The present invention relates to an amplifier circuit.
A semiconductor integrated circuit (hereafter referred to as an IC) that processes analog signals is often provided with an amplifier circuit. Various types of amplifier circuits have been developed to meet requirements corresponding to different purposes of use, and among them, the grounded emitter-type amplifier circuit is one of those that can be achieved through the simplest circuit structure. FIG. 8 illustrates the grounded emitter-type amplifier circuit 101 in the prior art.
An input terminal "in" of the amplifier circuit 101 is connected to a base terminal of an amplifying transistor Tr. Its output terminal "out" is connected to both a collector terminal of the amplifying transistor Tr and the source Vcc via a load resistor RLD. An emitter terminal of the amplifying transistor Tr is connected to the ground GND via a feedback resistor RE.
The amplifier circuit 101 structured as described above multiplies a base current ib that is caused to flow into the base terminal by an input voltage ei by a factor of hfe (the current amplification factor of the amplifying transistor Tr) and supplies a collector current ic (=hfe.times.ib) to the collector terminal. In addition, it outputs an output voltage eo at a value achieved by subtracting the product of the collector current ic and the load resistance RLD from the voltage supplied by the source Vcc. It is to be noted that the feedback resistor RE fulfills a function of stabilizing the collector current ic when a load fluctuation occurs at a circuit connected to the output terminal "out" or when a fluctuation occurs in the ambient temperature.
Now, the IC manufacturing process includes an inspection step implemented to improve production throughput, to assure product reliability, to screen good/defective chip products and the like. During the inspection step, a probe test is normally conducted on ICs to measure their electrical characteristics. In this probe test, the electrical characteristics of the ICs are measured by placing probes on the bonding pads of a wafer where the ICs are formed.
However, during such a probe test on ICs, noise attributable to the parasitic capacity component present in the test apparatus and the like may enter the ICs. In particular, in an IC provided with an amplifier circuit such as the amplifier circuit 101, such noise may cause the amplifier circuit to oscillate. Such oscillation of the amplifier circuit, which constitutes an erroneous operation of the IC, often results in difficulty in obtaining accurate electrical characteristics of the IC having the amplifier circuit through a probe test.